mikester said:
Assuming your pH is really that high and it's not just a measuring issue, then one thing you can try is adding vinegar to your kalk mix. The acid in the vinegar will help to bring down the pH of the kalk.
I'm not sure about the lowering of the kalk pH but adding vinegar does help. What it does is adds CO2 to the mixture, which helps dissolve the Calcium hydroxide. This way, when you drip it, it is already better dissolved, which means that it will use less CO2 that is dissolved in your tank water , which means your pH will not rise as much because CO2 helps to lower pH.
Also, I would only drip it at night.
You can make a farely cheap buffer using baking soda(sodium bicarbonate) and soda ash(can get from pool supply store). Mix it up in a 6 to 1 ratio (6 parts sodium bicarb to 1 part soda ash). I can't remember the dosage off hand, but if you want I can find it out for you.
HTH